607 lines
14 KiB
Go
607 lines
14 KiB
Go
// Copyright 2013 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Writing of Go object files.
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//
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// Originally, Go object files were Plan 9 object files, but no longer.
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// Now they are more like standard object files, in that each symbol is defined
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// by an associated memory image (bytes) and a list of relocations to apply
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// during linking. We do not (yet?) use a standard file format, however.
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// For now, the format is chosen to be as simple as possible to read and write.
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// It may change for reasons of efficiency, or we may even switch to a
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// standard file format if there are compelling benefits to doing so.
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// See golang.org/s/go13linker for more background.
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//
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// The file format is:
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//
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// - magic header: "\x00\x00go17ld"
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// - byte 1 - version number
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// - sequence of strings giving dependencies (imported packages)
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// - empty string (marks end of sequence)
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// - sequence of symbol references used by the defined symbols
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// - byte 0xff (marks end of sequence)
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// - sequence of integer lengths:
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// - total data length
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// - total number of relocations
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// - total number of pcdata
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// - total number of automatics
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// - total number of funcdata
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// - total number of files
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// - data, the content of the defined symbols
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// - sequence of defined symbols
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// - byte 0xff (marks end of sequence)
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// - magic footer: "\xff\xffgo17ld"
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//
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// All integers are stored in a zigzag varint format.
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// See golang.org/s/go12symtab for a definition.
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//
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// Data blocks and strings are both stored as an integer
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// followed by that many bytes.
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//
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// A symbol reference is a string name followed by a version.
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//
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// A symbol points to other symbols using an index into the symbol
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// reference sequence. Index 0 corresponds to a nil LSym* pointer.
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// In the symbol layout described below "symref index" stands for this
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// index.
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//
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// Each symbol is laid out as the following fields (taken from LSym*):
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//
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// - byte 0xfe (sanity check for synchronization)
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// - type [int]
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// - name & version [symref index]
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// - flags [int]
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// 1<<0 dupok
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// 1<<1 local
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// 1<<2 add to typelink table
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// - size [int]
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// - gotype [symref index]
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// - p [data block]
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// - nr [int]
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// - r [nr relocations, sorted by off]
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//
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// If type == STEXT, there are a few more fields:
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//
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// - args [int]
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// - locals [int]
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// - nosplit [int]
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// - flags [int]
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// 1<<0 leaf
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// 1<<1 C function
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// 1<<2 function may call reflect.Type.Method
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// - nlocal [int]
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// - local [nlocal automatics]
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// - pcln [pcln table]
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//
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// Each relocation has the encoding:
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//
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// - off [int]
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// - siz [int]
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// - type [int]
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// - add [int]
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// - sym [symref index]
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//
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// Each local has the encoding:
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//
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// - asym [symref index]
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// - offset [int]
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// - type [int]
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// - gotype [symref index]
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//
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// The pcln table has the encoding:
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//
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// - pcsp [data block]
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// - pcfile [data block]
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// - pcline [data block]
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// - npcdata [int]
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// - pcdata [npcdata data blocks]
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// - nfuncdata [int]
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// - funcdata [nfuncdata symref index]
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// - funcdatasym [nfuncdata ints]
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// - nfile [int]
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// - file [nfile symref index]
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//
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// The file layout and meaning of type integers are architecture-independent.
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//
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// TODO(rsc): The file format is good for a first pass but needs work.
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// - There are SymID in the object file that should really just be strings.
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package obj
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import (
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"bufio"
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"fmt"
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"log"
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"path/filepath"
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"sort"
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"github.com/google/gops/internal/dwarf"
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"github.com/google/gops/internal/sys"
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)
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// The Go and C compilers, and the assembler, call writeobj to write
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// out a Go object file. The linker does not call this; the linker
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// does not write out object files.
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func Writeobjdirect(ctxt *Link, b *bufio.Writer) {
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Flushplist(ctxt)
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WriteObjFile(ctxt, b)
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}
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// objWriter writes Go object files.
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type objWriter struct {
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wr *bufio.Writer
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ctxt *Link
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// Temporary buffer for zigzag int writing.
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varintbuf [10]uint8
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// Provide the the index of a symbol reference by symbol name.
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// One map for versioned symbols and one for unversioned symbols.
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// Used for deduplicating the symbol reference list.
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refIdx map[string]int
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vrefIdx map[string]int
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// Number of objects written of each type.
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nRefs int
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nData int
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nReloc int
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nPcdata int
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nAutom int
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nFuncdata int
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nFile int
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}
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func (w *objWriter) addLengths(s *LSym) {
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w.nData += len(s.P)
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w.nReloc += len(s.R)
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if s.Type != STEXT {
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return
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}
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pc := s.Pcln
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data := 0
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data += len(pc.Pcsp.P)
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data += len(pc.Pcfile.P)
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data += len(pc.Pcline.P)
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for i := 0; i < len(pc.Pcdata); i++ {
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data += len(pc.Pcdata[i].P)
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}
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w.nData += data
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w.nPcdata += len(pc.Pcdata)
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autom := 0
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for a := s.Autom; a != nil; a = a.Link {
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autom++
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}
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w.nAutom += autom
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w.nFuncdata += len(pc.Funcdataoff)
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w.nFile += len(pc.File)
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}
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func (w *objWriter) writeLengths() {
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w.writeInt(int64(w.nData))
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w.writeInt(int64(w.nReloc))
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w.writeInt(int64(w.nPcdata))
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w.writeInt(int64(w.nAutom))
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w.writeInt(int64(w.nFuncdata))
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w.writeInt(int64(w.nFile))
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}
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func newObjWriter(ctxt *Link, b *bufio.Writer) *objWriter {
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return &objWriter{
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ctxt: ctxt,
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wr: b,
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vrefIdx: make(map[string]int),
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refIdx: make(map[string]int),
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}
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}
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func WriteObjFile(ctxt *Link, b *bufio.Writer) {
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w := newObjWriter(ctxt, b)
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// Magic header
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w.wr.WriteString("\x00\x00go17ld")
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// Version
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w.wr.WriteByte(1)
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// Autolib
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for _, pkg := range ctxt.Imports {
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w.writeString(pkg)
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}
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w.writeString("")
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// Symbol references
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for _, s := range ctxt.Text {
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w.writeRefs(s)
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w.addLengths(s)
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}
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for _, s := range ctxt.Data {
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w.writeRefs(s)
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w.addLengths(s)
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}
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// End symbol references
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w.wr.WriteByte(0xff)
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// Lengths
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w.writeLengths()
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// Data block
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for _, s := range ctxt.Text {
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w.wr.Write(s.P)
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pc := s.Pcln
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w.wr.Write(pc.Pcsp.P)
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w.wr.Write(pc.Pcfile.P)
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w.wr.Write(pc.Pcline.P)
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for i := 0; i < len(pc.Pcdata); i++ {
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w.wr.Write(pc.Pcdata[i].P)
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}
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}
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for _, s := range ctxt.Data {
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w.wr.Write(s.P)
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}
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// Symbols
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for _, s := range ctxt.Text {
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w.writeSym(s)
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}
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for _, s := range ctxt.Data {
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w.writeSym(s)
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}
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// Magic footer
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w.wr.WriteString("\xff\xffgo17ld")
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}
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// Symbols are prefixed so their content doesn't get confused with the magic footer.
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const symPrefix = 0xfe
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func (w *objWriter) writeRef(s *LSym, isPath bool) {
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if s == nil || s.RefIdx != 0 {
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return
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}
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var m map[string]int
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switch s.Version {
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case 0:
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m = w.refIdx
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case 1:
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m = w.vrefIdx
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default:
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log.Fatalf("%s: invalid version number %d", s.Name, s.Version)
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}
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idx := m[s.Name]
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if idx != 0 {
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s.RefIdx = idx
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return
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}
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w.wr.WriteByte(symPrefix)
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if isPath {
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w.writeString(filepath.ToSlash(s.Name))
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} else {
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w.writeString(s.Name)
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}
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w.writeInt(int64(s.Version))
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w.nRefs++
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s.RefIdx = w.nRefs
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m[s.Name] = w.nRefs
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}
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func (w *objWriter) writeRefs(s *LSym) {
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w.writeRef(s, false)
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w.writeRef(s.Gotype, false)
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for i := range s.R {
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w.writeRef(s.R[i].Sym, false)
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}
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if s.Type == STEXT {
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for a := s.Autom; a != nil; a = a.Link {
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w.writeRef(a.Asym, false)
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w.writeRef(a.Gotype, false)
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}
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pc := s.Pcln
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for _, d := range pc.Funcdata {
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w.writeRef(d, false)
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}
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for _, f := range pc.File {
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w.writeRef(f, true)
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}
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}
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}
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func (w *objWriter) writeSymDebug(s *LSym) {
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ctxt := w.ctxt
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fmt.Fprintf(ctxt.Bso, "%s ", s.Name)
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if s.Version != 0 {
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fmt.Fprintf(ctxt.Bso, "v=%d ", s.Version)
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}
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if s.Type != 0 {
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fmt.Fprintf(ctxt.Bso, "t=%d ", s.Type)
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}
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if s.DuplicateOK() {
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fmt.Fprintf(ctxt.Bso, "dupok ")
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}
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if s.CFunc() {
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fmt.Fprintf(ctxt.Bso, "cfunc ")
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}
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if s.NoSplit() {
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fmt.Fprintf(ctxt.Bso, "nosplit ")
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}
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fmt.Fprintf(ctxt.Bso, "size=%d", s.Size)
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if s.Type == STEXT {
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fmt.Fprintf(ctxt.Bso, " args=%#x locals=%#x", uint64(s.Args), uint64(s.Locals))
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if s.Leaf() {
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fmt.Fprintf(ctxt.Bso, " leaf")
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}
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}
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fmt.Fprintf(ctxt.Bso, "\n")
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for p := s.Text; p != nil; p = p.Link {
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fmt.Fprintf(ctxt.Bso, "\t%#04x %v\n", uint(int(p.Pc)), p)
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}
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var c int
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var j int
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for i := 0; i < len(s.P); {
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fmt.Fprintf(ctxt.Bso, "\t%#04x", uint(i))
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for j = i; j < i+16 && j < len(s.P); j++ {
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fmt.Fprintf(ctxt.Bso, " %02x", s.P[j])
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}
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for ; j < i+16; j++ {
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fmt.Fprintf(ctxt.Bso, " ")
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}
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fmt.Fprintf(ctxt.Bso, " ")
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for j = i; j < i+16 && j < len(s.P); j++ {
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c = int(s.P[j])
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if ' ' <= c && c <= 0x7e {
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fmt.Fprintf(ctxt.Bso, "%c", c)
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} else {
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fmt.Fprintf(ctxt.Bso, ".")
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}
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}
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fmt.Fprintf(ctxt.Bso, "\n")
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i += 16
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}
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sort.Sort(relocByOff(s.R)) // generate stable output
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for _, r := range s.R {
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name := ""
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if r.Sym != nil {
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name = r.Sym.Name
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} else if r.Type == R_TLS_LE {
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name = "TLS"
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}
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if ctxt.Arch.InFamily(sys.ARM, sys.PPC64) {
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fmt.Fprintf(ctxt.Bso, "\trel %d+%d t=%d %s+%x\n", int(r.Off), r.Siz, r.Type, name, uint64(r.Add))
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} else {
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fmt.Fprintf(ctxt.Bso, "\trel %d+%d t=%d %s+%d\n", int(r.Off), r.Siz, r.Type, name, r.Add)
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}
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}
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}
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func (w *objWriter) writeSym(s *LSym) {
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ctxt := w.ctxt
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if ctxt.Debugasm != 0 {
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w.writeSymDebug(s)
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}
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w.wr.WriteByte(symPrefix)
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w.writeInt(int64(s.Type))
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w.writeRefIndex(s)
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flags := int64(0)
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if s.DuplicateOK() {
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flags |= 1
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}
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if s.Local() {
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flags |= 1 << 1
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}
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if s.MakeTypelink() {
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flags |= 1 << 2
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}
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w.writeInt(flags)
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w.writeInt(s.Size)
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w.writeRefIndex(s.Gotype)
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w.writeInt(int64(len(s.P)))
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w.writeInt(int64(len(s.R)))
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var r *Reloc
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for i := 0; i < len(s.R); i++ {
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r = &s.R[i]
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w.writeInt(int64(r.Off))
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w.writeInt(int64(r.Siz))
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w.writeInt(int64(r.Type))
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w.writeInt(r.Add)
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w.writeRefIndex(r.Sym)
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}
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if s.Type != STEXT {
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return
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}
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w.writeInt(int64(s.Args))
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w.writeInt(int64(s.Locals))
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if s.NoSplit() {
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w.writeInt(1)
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} else {
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w.writeInt(0)
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}
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flags = int64(0)
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if s.Leaf() {
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flags |= 1
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}
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if s.CFunc() {
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flags |= 1 << 1
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}
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if s.ReflectMethod() {
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flags |= 1 << 2
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}
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w.writeInt(flags)
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n := 0
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for a := s.Autom; a != nil; a = a.Link {
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n++
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}
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w.writeInt(int64(n))
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for a := s.Autom; a != nil; a = a.Link {
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w.writeRefIndex(a.Asym)
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w.writeInt(int64(a.Aoffset))
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if a.Name == NAME_AUTO {
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w.writeInt(A_AUTO)
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} else if a.Name == NAME_PARAM {
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w.writeInt(A_PARAM)
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} else {
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log.Fatalf("%s: invalid local variable type %d", s.Name, a.Name)
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}
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w.writeRefIndex(a.Gotype)
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}
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pc := s.Pcln
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w.writeInt(int64(len(pc.Pcsp.P)))
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w.writeInt(int64(len(pc.Pcfile.P)))
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w.writeInt(int64(len(pc.Pcline.P)))
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w.writeInt(int64(len(pc.Pcdata)))
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for i := 0; i < len(pc.Pcdata); i++ {
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w.writeInt(int64(len(pc.Pcdata[i].P)))
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}
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w.writeInt(int64(len(pc.Funcdataoff)))
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for i := 0; i < len(pc.Funcdataoff); i++ {
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w.writeRefIndex(pc.Funcdata[i])
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}
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for i := 0; i < len(pc.Funcdataoff); i++ {
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w.writeInt(pc.Funcdataoff[i])
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}
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w.writeInt(int64(len(pc.File)))
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for _, f := range pc.File {
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w.writeRefIndex(f)
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}
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}
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func (w *objWriter) writeInt(sval int64) {
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var v uint64
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uv := (uint64(sval) << 1) ^ uint64(sval>>63)
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p := w.varintbuf[:]
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for v = uv; v >= 0x80; v >>= 7 {
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p[0] = uint8(v | 0x80)
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p = p[1:]
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}
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p[0] = uint8(v)
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p = p[1:]
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w.wr.Write(w.varintbuf[:len(w.varintbuf)-len(p)])
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}
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func (w *objWriter) writeString(s string) {
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w.writeInt(int64(len(s)))
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w.wr.WriteString(s)
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}
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func (w *objWriter) writeRefIndex(s *LSym) {
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if s == nil {
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w.writeInt(0)
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return
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}
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if s.RefIdx == 0 {
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log.Fatalln("writing an unreferenced symbol", s.Name)
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}
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w.writeInt(int64(s.RefIdx))
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}
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// relocByOff sorts relocations by their offsets.
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type relocByOff []Reloc
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func (x relocByOff) Len() int { return len(x) }
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func (x relocByOff) Less(i, j int) bool { return x[i].Off < x[j].Off }
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func (x relocByOff) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
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// implement dwarf.Context
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type dwCtxt struct{ *Link }
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func (c dwCtxt) PtrSize() int {
|
|
return c.Arch.PtrSize
|
|
}
|
|
func (c dwCtxt) AddInt(s dwarf.Sym, size int, i int64) {
|
|
ls := s.(*LSym)
|
|
ls.WriteInt(c.Link, ls.Size, size, i)
|
|
}
|
|
func (c dwCtxt) AddBytes(s dwarf.Sym, b []byte) {
|
|
ls := s.(*LSym)
|
|
ls.WriteBytes(c.Link, ls.Size, b)
|
|
}
|
|
func (c dwCtxt) AddString(s dwarf.Sym, v string) {
|
|
ls := s.(*LSym)
|
|
ls.WriteString(c.Link, ls.Size, len(v), v)
|
|
ls.WriteInt(c.Link, ls.Size, 1, 0)
|
|
}
|
|
func (c dwCtxt) SymValue(s dwarf.Sym) int64 {
|
|
return 0
|
|
}
|
|
func (c dwCtxt) AddAddress(s dwarf.Sym, data interface{}, value int64) {
|
|
rsym := data.(*LSym)
|
|
ls := s.(*LSym)
|
|
size := c.PtrSize()
|
|
ls.WriteAddr(c.Link, ls.Size, size, rsym, value)
|
|
}
|
|
func (c dwCtxt) AddSectionOffset(s dwarf.Sym, size int, t interface{}, ofs int64) {
|
|
ls := s.(*LSym)
|
|
rsym := t.(*LSym)
|
|
ls.WriteAddr(c.Link, ls.Size, size, rsym, ofs)
|
|
r := &ls.R[len(ls.R)-1]
|
|
r.Type = R_DWARFREF
|
|
}
|
|
|
|
func gendwarf(ctxt *Link, text []*LSym) []*LSym {
|
|
dctxt := dwCtxt{ctxt}
|
|
var dw []*LSym
|
|
|
|
for _, s := range text {
|
|
dsym := Linklookup(ctxt, dwarf.InfoPrefix+s.Name, int(s.Version))
|
|
if dsym.Size != 0 {
|
|
continue
|
|
}
|
|
dw = append(dw, dsym)
|
|
dsym.Type = SDWARFINFO
|
|
dsym.Set(AttrDuplicateOK, s.DuplicateOK())
|
|
var vars dwarf.Var
|
|
var abbrev int
|
|
var offs int32
|
|
for a := s.Autom; a != nil; a = a.Link {
|
|
switch a.Name {
|
|
case NAME_AUTO:
|
|
abbrev = dwarf.DW_ABRV_AUTO
|
|
offs = a.Aoffset
|
|
if ctxt.FixedFrameSize() == 0 {
|
|
offs -= int32(ctxt.Arch.PtrSize)
|
|
}
|
|
if Framepointer_enabled(GOOS, GOARCH) {
|
|
offs -= int32(ctxt.Arch.PtrSize)
|
|
}
|
|
|
|
case NAME_PARAM:
|
|
abbrev = dwarf.DW_ABRV_PARAM
|
|
offs = a.Aoffset + int32(ctxt.FixedFrameSize())
|
|
|
|
default:
|
|
continue
|
|
}
|
|
typename := dwarf.InfoPrefix + a.Gotype.Name[len("type."):]
|
|
dwvar := &dwarf.Var{
|
|
Name: a.Asym.Name,
|
|
Abbrev: abbrev,
|
|
Offset: int32(offs),
|
|
Type: Linklookup(ctxt, typename, 0),
|
|
}
|
|
dws := &vars.Link
|
|
for ; *dws != nil; dws = &(*dws).Link {
|
|
if offs <= (*dws).Offset {
|
|
break
|
|
}
|
|
}
|
|
dwvar.Link = *dws
|
|
*dws = dwvar
|
|
}
|
|
dwarf.PutFunc(dctxt, dsym, s.Name, s.Version == 0, s, s.Size, vars.Link)
|
|
}
|
|
return dw
|
|
}
|